Medical sophistication enables a higher level of medical treatment. However, advanced treatment for a serious disease is very expensive, and not everybody can afford it. Against this backdrop, there arises a need for preventive medicine and early disease detection that are easily available to everybody before large-scale treatment. Facilitating disease examination by a simpler test that is possible even at home makes it possible to detect a disease in its early stage and thus obtain a wide choice of options of medical operations and avoid the problem of high medical expenses.
However, relatively inexpensive tests as in today's physical checkups are not sufficient for discovery of serious diseases. It is more demanded to detect serious diseases at the inspection level of the physical checkup.
A biosensor has been studied as a device capable of implementing such a simple test in the future. There are various kinds and definitions of biosensors in this world. In this specification, the biosensor is defined as “a device that arranges a substance having biological information on a portable chip and performs some detection processing for the chip, thereby determining the biological information”.
Such an ideal sensor is still in the research stage. Fundamental researches toward actualization include following related arts 1 to 3.
(Related Art 1: Label-Type Biosensor)
There is a specimen identification device such as a biosensor using magnetic beads to identify a specimen, which has been studied to identify a specimen, for example, a biological substance such as a protein or a DNA more easily than fluorometry currently in use. If a protein can easily be identified by a test on the chip, it may be possible to easily identify the biological substance at a clinic without using a bulky device. This specimen identification device features using the magnetic beads as a label in place of the conventional fluorescent substance. Detecting a magnetic field allows to perform specimen identification at a sensitivity higher than before. The conventional biosensor using magnetic beads as a label is known in U.S. Patent Application Publication 2008/0255006 and in D. R. Baselt, U.S. Pat. No. 5,981,297 (Nov. 9, 1999), “Biosensor using magnetically-detected label”.
(Related Art 2: Label-Free Biospecimen Method)
As a medical determination technology that is an amalgam of state-of-the-art engineering and medical care, an attempt to obtain biological information without using a label by irradiating a biological substance with a special wave has been proposed in Appl. Phys. Lett. 80, 1, 154 (2002), “Integrated THz technology for label-free genetic diagnostics”, JP-A 2006-153852 (KOKAI), and JP-A 2007-10366 (KOKAI).
(Related Art 3: Oscillator Using Spin Torque Effect)
As a device capable of oscillating a high frequency at room temperature, an STO (Spin Torque Oscillator) using the spin-torque effect has been proposed in J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996), and a lot of theoretical and experimental examinations have been made. This document is known as the first paper that has introduced the basic concept. Actual experimental verifications have been done since then, in a document such as S. I. Kiselev et al, Nature 425, 308 (2003) and many groups following it to reveal that using the spin-torque effect allows to oscillate at a frequency of several GHz.
There is proposed a variation of the STO proposed in M. A. Hoefer et al, Phys. Rev. Lett. 95, 267206 (2005), “Theory of magnetodynamics induced by spin-torque in perpendicularly magnetized thin films”, which readily oscillates by adopting a structure including a number of nano-size current path portions so as to improve the local current density.
The detection method using a label such as magnetic beads is too complex to enable early determination not in a large medical institution but at a simple clinic in town and in turn at home, and diagnosis at home is therefore very difficult. However, there is no label-free biosensor capable of easily doing specimen identification on a chip.
On the other hand, a label-free diagnosis method using THz waves exists. This method requires a bulky device to oscillate a THz wave, and diagnosis at home is more difficult than that using the biosensor using magnetic beads. That is, to allow diagnosis at home, a label-free specimen identification method is necessary. However, the THz wave suitable for label-free identification cannot be oscillated on a chip.
A GHz-order oscillator implementable on a chip exists as a conventional technique. However, implementation of THz oscillation is supposed to be difficult.